New Roof Guide

A guide to installing a new roof

This article will show you some of the main decisions and choices that will affect the quality and cost of your roof. Before we get down to the nitty gritty of actual roofing prices please be patient, take 5 minutes to read this article and understand a little about what you’re buying, and how the choices you make will affect your new roof.

New roof choices

Lets face it you wouldn’t buy a new car from a salesman in a show room based on colour alone would you, or if you didn’t know how many doors or wheels you wanted ? No that would be silly, but a new roof will cost you quite a bit of your hard earned money, and If you know what questions to ask, it just might stop you buying an overpriced crap roof… Blunt but true.

Not only have I been fitting new roofs for over 30 years but repairing them also, often shoddy workmanship is to blame for many bad roofs, but this can also be compounded by a lack of understanding of what questions to ask a potential roofing contractor by the customer. This guide to buying a new roof should help advise you on what questions to ask your roofing contractor.

New roof checklist

Before thinking of any roof replacement there are some important things you really should consider. Below I have listed the top ten questions I would ask a roofer about a potential new roof.

Top 10 questions to ask a roofing contractor about you’re new roof…

Can you check my roof structure inside to make sure it is sound

What is the condition of my current roof and can I reuse the slate or tiles if I want to ? If so what percentage do you think is reusable

Will my new roofs weight have a negative impact on the strength of my roof structure

Do I require planning permission

How will you join to my neighbour’s roof (if applicable)

Will you be replacing valleys and flashings, if so what with

Do I need, or do you recommend roof ventilation

On roof pitches below 30 degrees, what undersarking and roof covering do you recommend

How long have you been in business, what is the guarantee, and what does the guarantee cover me for

Are you Insured to work on my property

How to ask roofing questions

Obviously standing in front of a roofer firing off questions one after another could make you look like an obsessive nutter, any tradesman now and again get’s rogue customers who are a pain to work for. You don’t want to appear like a rogue customer, so allow the roofing contractor to offer up as much of this information as possible during normal conversation, if you appear friendly and approachable many of these points will come up anyway during normal flowing conversation. Listen to what they say and steer the conversation towards items that may interest you.

Quality roofing – Most good tradesmen like a customer to be interested in their work and the quality of the finish and normally take pride in it, so they actually like to be asked. I know I personally give an internal sigh of relief that someones interested.

Roof covering choices

From new the most common choices in the UK are… Concrete tiles, Slates – both natural and man made, and fired clay tiles. New tiles and slates often come with a manufacturers or merchants guarantee, that is in addition to the guarantee of craftsmanship and fitting by your chosen roofing contractor.

Re using your existing slates or tiles

If your existing roof has Slate, Clay tiles or Handmade clay tiles it can be an option to re-use and re-lay them onto your new roof if they are in good condition. This can be very desirable to keep the period look of a property whilst still achieving a new guaranteed roof with a lifespan of 80 years or over. If the slates are in good condition and can be used again, this will obviously save you from buying all new slates and this will make the material costs cheaper.

Re using slates

Natural Slate – Slates are the most common roofing material to be re used, get your ‘would be’ roofing contractors to check and assess the condition of the slate for splits and quality. It is quite common to get a reusable figure of around 70% for the slate already nailed to your roof as long and there is nothing wrong with it.

Any missing slates can be purchased by yourself or the roofer from a roofing merchant in his reclamation section, second hand slates reclaimed from re-roofs is a busy and thriving market, so you will have no problem sourcing matching slate.

Re using clay tiles

Just because your current roof is old or original that doesn’t always mean it needs fully replacing, a good example of this is with fired clay tiles like Rosemary tiles, Acme tiles or Dreadnaught tiles to name just three.

Clay tiles – Fired clay tiles, hand made or machine made can also be used again depending on condition. Things to look for are softness or flaking. Flaking is normally evident on the top surface of the tile or they can look like scabs of tile that fall down the roof. Tile softness or brittleness mostly only affects the handmade tiles.

Again get a roofer to check the condition of the tiles for viability, but if you have been lucky to get a good well fired batch in the first place, there is no reason they cannot be used again.

Re using concrete roof tiles

Concrete tiles are very common now in the U.K. and rightly so, when laid properly and in a sympathetic manner they are both pretty to look at and practical. The lifespan of a concrete tile should be over 60 years before they start to wear thin.

Concrete tiles – Unless they are relatively new and in good condition, do not re-use concrete roof tiles, especially if older that 20 years. Concrete tiles are a great roof covering when new, but wear thin and become brittle with the passage of time and weathering.

Unfortunately weathering to the top surface of a concrete tile over its first few decades of life, leaves it open to moss, lichen build up, or surface abrasion. It’s very questionable economy to spend a lot of money re-using a part worn tile product in this case, even though it is possible.

Internal roof structure

Make sure that the roofing contractors check the internal timber structure of your roof, this is to make sure that there are no problems that need to be addressed like roof sag, roof spread or incorrectly supported roof purlins. This is especially true in traditionally constructed roofs, and it’s comparatively cheap to fix roof problems like this when the roof is stripped and ready for re-roofing rather than after the event. Also if you are considering a heavier roof covering, like swapping from a slate roof to concrete tiles, make sure no additional support timbers or upgrades to roof structure are required, otherwise your roof may acquire roof sag or roof spread later on.

Roof timbers – Unsupported roof purlins, just one example of an easy to fix problem that could need to be addressed before the new roof goes on.

Roof pitch or roof angle

Every roof covering has a minimum pitch or slope unless it’s a flat roof. If you have a shallow pitched roof i.e. below 30 degrees of slope, consideration will have to be made on the type of roof covering that you’re going to use. Commonly, roof tiles will allow for a shallower pitch, sometimes as low as 12.5 degrees for certain makes of roof tile as compared to 20 – 22.5 degrees for selected slates.

I have seen a lot of people come unstuck with leaking shallow pitched roofs, not only do you need the slate or tile to match the pitch, but it also needs the correct amount of overlap or headlap, as well as a good quality undersarking. Unfortunately weather conditions like wind and rain can drive water under a shallow pitched roof if you don’t get it right.

Low angle roof – In a situation where you’re building a new shallow sloping roof, make sure someone makes an effort to measure the finished slope properly before it’s tiled or slated. There are very good mobile phone apps that will do this for you these days, mistakes can be made whilst following plans, even by planning inspectors.

Undersarking – Membrane or Felt

Undersarking provides a secondary line of defence against water ingress in exceptional circumstances and should NOT be relied upon to keep water out, the roof covering should do that 99.9% of the time.

Undersarking – The generic term used for a waterproofing layer underneath the top roof covering of tiles, slates, etc. Commonly breathable roofing membrane is used these days or sometimes under tillers or under slaters felt called 1F is used.

If you have a shallow pitched roof only the best quality breathable roofing membrane should be used or ‘1F’ under felt or similar, ask roofing contractors about their recommendations for situations like these.

Joining two roofs together

This will be necessary where your roof meets a neighbouring roof, sometimes you may need to join onto your neighbours roof, or you may have an adjoining roof yourself that you wish to keep. This can occur when a slate roof meets tiles, artificial slates, different sized slates or you’re joining two non matching tile profiles. If you need to use bonding gutters it will push up the price of your new roof a little, as fitting them is time consuming even though they are cheap to buy.

Bonding gutter explained – If you are joining two different types of roof together you will need to use a special roof joint called a bonding gutter, this is also sometimes referred to as a bonding valley, secret gutter or secret valley.

Join two roofs – This is a video of how to fit a bonding gutter for those who may be interested in what’s involved.

Unfortunately some roofers do not fit these as they are time consuming to fit ,and as we all know time is money, so instead they join onto next door’s roof with a simple overlap of a sand and cement mortar bed only. This is totally wrong and will leak after a few years if not straight away, it usually leads to expensive repairs, damaged ceilings and re-decoration, oh… and grumpy neighbours in my experience.

Joining two similar roofs together

The preferable way to join one roof onto another is to use similar slates or tiles, not only will it make the join easier on the eye but easier on the pocket too.

Joining similar roofs – If you use similar sized or the same profiled tiles or slates it is possible to blend one roof into another, this will make life easier for the roofer and therefore cheaper for you.

Lead valleys

Lead valleys are a way of joining one roof to another or separating two roof angles, and they should be treated exactly the same as lead flashings above. If you have existing lead valleys and you’re having a new roof do not re-use the old lead, it really is false economy.

Lead and GRP valleys compared – There’s very little difference between these two from floor level, and both will last a very long time if well fitted. GRP valleys do tend to leak more in later life depending on the quality of the valley and the quality of the installer.

Fibreglass GRP valleys

Fibreglass valleys are the modern alternative to lead, its not better but it is cheaper. With the average material cost of milled lead at say £100 for a medium sized roof valley, a fiberglass valley the same size could cost as little as £10. Now if you imagine this saving scaled up over many houses, it goes some way to explaining why they are so popular on large new build housing estates. If you are going to use fibreglass valleys I would still recommend the roofer installs valley boards, should anyone have to walk up, or work on the valley at a later stage, a foot will not shatter or go through the valley if is supported by valley boards. This is a simple step that is left out 90% of the time.

Lead flashings

Check to see if you will be getting new roof flashings or lead flashings. All good roofers will renew them automatically, but on numerous occasions I have seen the old lead flashings from the previous roof re-used to save on lead costs and labour.

Lead flashing -Typically a roofer could save a days labour plus lead costs by using the old lead flashings, but as they have already probably done a 50 to 100 years service its never a good idea to use them. Lead wears thin and splits with age, don’t use it again.

Lead flashing alternatives can be used like the one in the picture above, keep in mind that it may be more expensive than lead to buy and fit, but of course there’s no scrap value to a thief if the roof is easily accessible from the ground.

Roof ventilation

People living in houses generate warm moist air from every day living, cooking, bathing and even breathing and will all contribute to this, and all that moisture wants to rise upwards or find a cold surface. Lofts can become damp and even mouldy if you don’t have sufficient air circulation and ventilation inside your roof space, so don’t forget to ask your potential roofers about roof vents, tile vents or slate vents to combat this.

I also have an article on common types of roof ventilation in case it is of any use.

Ridge tiles

Ridge tiles or hip ridges sit on the top edges of a roof and provide a waterproof capping between one elevation of a roof and another i.e. on the top of a roof between a front and back roof.

Ridge tiles – These can be fixed in the traditional manner where they sit on a bed of strong mortar, or via a newer dry ridge system. Dry ridge is a method of mechanical fixing by clips or screws that do not require a wet mortar mix. Either technique if done correctly will provide many years of trouble free service.

These days dry ridge systems are compulsory on all new roofs, unless special circumstances prevail like some period properties, handmade tiles or listed buildings when traditional mortar may be used instead. Even then it can be a combination of mortar with mechanical fixings as well.

Verges and Gable ends

Verges are the name given to the finish at the end of a roof, most commonly seen at a gable end. Mortar bedded verges tend to be cheaper than a correctly installed dry verge system.

Gable end verges – Here are two common types, the traditional mortar finish (bedded verge) or a newer dry verge system or cloaked verge. Both provide an excellent finish as long as they are done properly. Some cheaper dry verge systems can be prone to insects finding their way in.

Anti pest measures

This is an important detail that sometimes gets forgotten at the very bottom of a tiled roof (eaves) . If you have any sort of roof tile with a profile that is not flat it may leave open ends for pests like birds or squirrels to get in.

Bird Combs – Make sure bird combs or eave fillers are used, and if you are prone to squirrels in your area ask a roofing contractor what he can recommend. Sometimes aluminium eave fillers can be sourced or open tile profiles can be filled with mortar. Bird combs are cheap to install and essential to stop pests and birds.

Planning permission

Do I need planning permission to change my roof ?

Yes, and No. If you are re roofing with a similar material and not changing the structure of your roof you should be OK, as long at the new roof isn’t heavier, significantly lighter or different in such a manner that it could cause movement to occur. If you are changing from, for instance, Slate to Tiles, this could be one of those situations and advice should be sought. Also keep in mind that local planning may forbid the change of a particular roofing material like local stone, local slate or thatching for a modern material. Ask your local roofing contractor about these issues as he should know about any regulations specific to your area. Also see the advice on the planning portal